Roof lining of a vehicle and a method for producing same

ABSTRACT

A multifunctional, lightweight and acoustically optimized interior lining for the roof of a vehicle is disclosed. The inventive lining comprises an air permeable core layer, a first stiffening layer, a second stiffening layer and a decor layer. Said layers are connected to one another by means of air permeable adhesive layers. The total air flow resistance of the second stiffening layer, decor layer, and attached adhesive layers, arranged on the side of the core layer facing the passenger compartment, is within the range of 500 Nsm −3 &gt;R t &lt;3500 Nsm −3 . The total surface area weight of said layers lies in the range of 300 to 800 gr/m 2 . A method for producing said lining and the use thereof in a roof of a vehicle are also disclosed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a roof lining for a vehicle roof, to amethod for producing the same and to the use thereof in a vehicle roof.

2. Description of the Related Art

Vehicle roof linings are important components for the interior lining ofvehicles. Essentially, they affect the acoustic characteristics of thevehicle, they should be aesthetically pleasing and should besufficiently stiff in order to support accessories such as, for example,sun visors, interior lighting, ventilation slits, clothes hooks etc.Furthermore these linings should be lightweight, should be economicallymanufacturable, should be easy to install, and should fulfil a number ofcriteria (fire resistance, emission of toxic or noxious fumes etc.).

Vehicle parts having large surface areas, in particular vehicle roofs,tend to vibrate on traveling on account of their low inherent stability.This behavior is conventionally counteracted by mounting dampingmaterial, in particular heavy layers containing bitumen. Traditionallymulti-layered roof lining elements are used which have only an aestheticfunction and serve to support accessories.

An acoustically effective roof lining is known, for example, from EP0,255,332, and comprises a semi-flexible carrier layer with which, inthe manner of a snap closure, the roof lining can be tensioned againstthe vehicle roof. With this carrier layer a classic spring-mass-systemwith a resilient, sound-absorbing foam layer and a visco-elastic,closed-pored heavy layer (filled with bitumen) is pressed against thevehicle roof.

EP 0,637,820 for example discloses a sound absorbing roof lining, whichessentially comprises an approximately 5–15 mm thick, semi-rigidpolyurethane (PU) foam layer and a 4–10 mm thick, spring elasticcompound fiber layer, both layers being permeable to air. In thisembodiment, the foam layer is reinforced on both its sides with glassfibers and, on the passenger compartment side, comprises an airpermeable décor layer. The individual layers are, in turn, connected toeach other by means of an air permeable adhesive layer, and inparticular by a PU-adhesive. However, this sound absorbent roof liningis a classical spring-mass-system or a classical foam absorber.

As it is the general aim of the automobile industry to reduce the weightof vehicles, these systems have proven to be too heavy for modernrequirements of the automobile industry. As a result, ever thinner andlighter lining elements are used, which however, have an insufficientacoustic effectiveness, for example for sound absorption purposes, andin particular in the range below 1000 Hz.

Multi-layered vehicle roof linings are also known which are lightweightand stiff, but which also have a poor acoustic performance.

Thus, FR 2,503,721 suggests a lightweight roof lining, which essentiallycomprises a porous and glass fiber reinforced foam layer being coveredwith a décor layer, and having an air-impermeable polyethylene foilbetween the décor layer and the glass fiber reinforced foam layer inorder to prevent the permeation/penetration of adhesive componentsthrough the décor layer. This foil results in an insufficient acousticabsorption capacity of the roof lining, which could possibly be improvedby applying perforations. However, such perforations in the polyethylenefoil can cause visually perceptible changes to the décor layer.

Therefore, in WO98/18657 there is described an ultra-light,multifunctional assembly, with which an excellent acoustic comfort inthe vehicle interior can be achieved, and at the same time achieving aweight reduction of about 50% in comparison to linings having a classicspring-mass-system and an improved aesthetic durability. Thispublication describes the composition of an acoustically andaesthetically satisfactory vehicle roof lining, however withoutdescribing the method of manufacture.

BRIEF SUMMARY OF THE INVENTION

It is therefore the object of the present invention to provide anultra-light vehicle roof lining of the new generation, which can bemanufactured simply and thus cost efficiently.

In particular it is the object of the present invention to provide avehicle roof lining which is light-weight, self-supporting, highlyacoustically effective, aesthetically pleasing and maintains itsaesthetic appearance. Furthermore, the inventive lining should be ableto be easily acoustically adjusted and should allow for as wide a rangeof various décor materials as possible.

It is thus also the object of the present invention to provide a methodfor manufacturing light-weight roof linings which can be variablydesigned so as to meet the desired acoustic and aesthetic requirements.

According to the invention this object is achieved by a lining with thefeatures of claim 1, which can be manufactured by a method according toclaim 10. In particular this multifunctional and lightweight innerlining has a multilayered structure and comprises an air impermeablecore layer, in particular comprising a thermoformed PU foam which isprovided on both its surfaces with an air permeable stiffening layer(which, in turn, can be composed of a number of layers).

On the passenger compartment side, this multilayered structure has anair permeable décor layer, whilst an air impermeable backing layer canbe arranged on the vehicle roof side. These layers are adhesed to eachother by thermoplastic, air permeable adhesive means. Between the décorlayer and the stiffening layer on the passenger compartment side a thinperforated foil is preferably used as adhesive means, which foilpartially opens during the manufacturing process and adheres to theadjacent layers. The air flow resistance of the layers which areadjacent the foamed core layer on the passenger compartment side can bespecifically and easily adjusted by choice of the composition andcompaction (spacial weight) of the stiffening layer and by suitablechoice of the adhesive layer and the décor layer, i.e. can be simply andcontrollably adjusted to the specific requirements. According to theinvention this combination of layers is composed such, that an air flowresistance of 500 Nsm⁻³<R_(t)<2500 Nsm^(−3,) and in particular 900Nsm⁻³<R_(t)<1900 Nsm⁻³ is achieved, whilst the area weight of thiscombination of layers is between 0.3 to 0.8 kg/m². For optimizing theacoustic efficiency of the vehicle roof lining it is essential that theair flow resistance of those layers on the passenger compartment sidewhich are arranged before the core layer lies within the desired range.The décor layer can be made of a nonwoven or some other air permeablematerial, for example a compacted textile with or without a thin,open-celled foam layer. Furthermore, it is essential for the acousticefficiency of the vehicle roof lining that, if the side facing the metalroofing sheet is sealed, the layer required for such sealing has a lowarea weight (less than 50 gr/m²) and that this layer is coupled to theother layers of the supporting structure in a suitable manner.

This vehicle roof lining distinguishes itself by its particularly goodacoustic performance and by the fact that it is self-supporting andultra-light.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 shows a preferred embodiment of the roof lining according to theinvention having the following sequence of layers:

1. an air impermeable nonwoven (about 0.04 kg/m²)

2. a thermoformable nonwoven (about 0.2 kg/m²)

3. an adhesive layer (reticulating adhesive)

4. a thermoformable PU foam core (about 20 mm thick, 0.2 kg/m²)

5. an adhesive layer (reticulating adhesive)

6. a thermoformable nonwoven (0.3 kg/m²)

7. a slitted PE-foil (about 50 μm) or a microporous adhesive fiber layer

8.a décor covering (nonwoven weighing about 0.2 kg/M²)

DETAILED DESCRIPTION OF THE INVENTION

The embodiment described above can easily be acoustically trimmed by theexpert without negatively influencing its advantageous effects. Inparticular, the thickness of the core layer 4 can be adjusted to meetthe requirements, i.e. to have a weight of less than 0.2 kg/M² up to aweight of more than 0.4 kg/M². The décor layer 8 can compriseimaginative textiles or layers having foram backing. The layers 5, 6, 7,8 on the passenger compartment side can be formed such that their airflow resistance meets the desired acoustic requirements. By varying thestiffening layer 2 on the metal roofing sheet side the stiffness of theentire lining can be adjusted as desired. A variation in the compositionof the stiffening layers 2 and 6 is also within the skill of the expert.Also any specific shaping of the roof lining and in particular aspecific surface pattern on the rear side of the lining can be freelychosen.

The inventive method for manufacturing such a roof lining has thefeatures of the present claim 10 and aims at providing a stack havingthe following sequence of layers:

-   -   an air impermeable backing layer;    -   a first air permeable, thermoformable nonwoven;    -   a first air permeable adhesive layer;    -   an air permeable, thermoformable PU foam core;    -   a second air permeable adhesive layer;    -   a second air permeable, thermoformable nonwoven;    -   a third air permeable adhesive layer;    -   an air permeable décor layer.

In a subsequent method step this stack is heated to a temperature ofabout 180° C. in order to soften the thermoplastic adhesive layers andin order to trigger a secondary reaction of the PU foam core. In a nextmethod step this heated stack is transferred into a cold moulding tooland there is brought into its desired shape whilst the secondaryreaction of the PU foam core is completed and the material stack iscooled to a temperature in the range of between 20° C. to 60° C.Subsequently the formed and bonded stack is cut into the desiredcontour.

This method of manufacture has proven to be advantageous in comparisonto conventional methods because by using a thermoformable PU foam coreand thermoplastically bonded stiffening layers the roof lining can beformed in a cold moulding tool, thus eliminating seepage of adhesivematerial. This method especially provides for rapidly transferring theheated stack into the cold moulding tool. Care is taken to minimize thedecrease in temperature during the transfer process and this decrease intemperature should amount to less than 20° C. on the stack-surfaces, andpreferably less than 10° C.

With this method, for example, a stack having a total thickness of 27 mmis heated to 180° C. For this purpose the stack can be pressed to atotal thickness of 22 mm. During this heating phase the adhesives beginto melt, on the one hand, and on the other hand a secondary reaction istriggered in the PU foam core. The cold moulding tool in which theheated stack is cooled within about 1 minute has a temperature ofbetween 20° C. and 60° C. During this cooling process the adhesivelayers having a reticulate and/or drop-like distribution harden andcause the adjacent layers to bond.

It is evident that this method of manufacture considerably reducesproduction costs. By using thermoformable foams or nonwovens it ispossible to make products which do not emit contaminants/noxiousmaterials. Furthermore, this method allows to dispense with liquidadhesives which lead to stains in the decor layer in conventional rooflinings. An essential advantage of the method according to the inventionlies in the fact that the acoustic features of the manufactured productscan be variably adjusted by means of a simple variation in the thicknessand composition of the individual layers or by variation in theperforation density of the adhesive layers. This permits the method tobe universally used, i.e. it is suitable for manufacturing differentlyarranged or dimensioned roof linings without having to rearrange theproduction line.

The roof lining manufactured according to the inventive method has allthe required advantageous features, and in particular it is lightweight,i.e. has a weight of merely about 1000 gr/m², it fulfils therequirements of the automobile industry with respect to the requiredinherent stiffness and form stability, and fulfils the regulationsconcerning fire resistance, toxic emissions and so forth. Furthermore,the roof lining according to the invention is not sensitive to humidity,is olfactorily neutral and inhibits fungal growth. The manufacturingmethod according to the invention is substantially simpler and thus moreeconomical than those currently known.

Preferred embodiments of the roof lining and the method according to theinvention show the features of the respective dependent claims.

The invention is explained in more detail by way of the single FIGUREand a description of an embodiment.

FIG. 1 is a schematic illustration of the structure of a lining elementaccording to the invention.

The exemplary embodiment of the roof lining 9 shown in FIG. 1 has atotal thickness of 20 mm. This lining has a central core layer 4 whichcomprises an air permeable material, preferably an open celledthermoformable PU foam. This foam layer 4 has a thickness of 20 mm andhas an area weight of 200 gr/m². A stiffening layer 2 respectively 6 isarranged on each side of this core layer 4. These stiffening layers areattached to the core layer 4 by means of an adhesive layer 3, 5. In thispreferred embodiment, a first stiffening layer 2 having an area weightof 200 gr/m² is arranged on the metal roofing sheet side and a secondstiffening layer 6 having an area weight of 300 gr/m² is arranged on thepassenger compartment side. It is to be understood that other suitable,that is stiff materials can be used for the stiffening layers. It isessential for the present invention that the individual layers describedabove are air permeable and that also the adhesive layers permit air toflow through. On the vehicle roof side there is arranged an airimpermeable backing layer 1, preferably an air-tight sealing nonwovenhaving an area weight of 40 gr/m². By means of this backing layer 1 airis prevented from flowing from the passenger compartment through the airpermeable lining 9 into the space between the vehicle roof A and thelining 9, which would lead to dirt accumulation. An air permeable decorlayer 8, for example a decor nonwoven having an area weight of 200 gr/m²is arranged on the passenger compartment side. Preferably, a slittedfoil 7 is disposed between the decor layer 8 and the second stiffeninglayer 6. This foil 7 opens when the entire stack is heated. Theperforation density thus achieved can easily be predetermined bysuitable arrangement and dimensioning of the perforations. The layersarranged on the passenger compartment side of the foam core are disposedin such a manner that on the passenger compartment side the lining hasan air flow resistance of 500 Nsm⁻³>R_(t)<3500 Nsm⁻³, and in particular900 Nsm⁻³<R_(t)<1900 Nsm⁻³, with an area weight of between 300 to 800gr/m². In a further preferred embodiment the backing layer 1 is composedof an air impermeable nonwoven or an air impermeable foil or of acombination of nonwoven and foil and is attached (dot-wise or partially)to the vehicle roof A in such a manner that the sound absorption of theroof lining is optimized. If a relief-like profile is embossed into thereverse side of the roof lining element, this profile can be utilizedfor the dot-like or line-like attachment of the sealing foil. Thisrelief-like profile of the reverse side of the lining in the mouldedstate causes the formation of a coherent thin and acoustically effectiveair layer between the roof lining and the metal roofing sheet. Thus, theroof lining has the effect of damping the oscillations of the metalroofing. The stiffening layers used in this preferred embodimentcomprise a mixed nonwoven into which, among other things, strengtheningfibers and/or fine or micro-fibers are admixed. These stiffening layerscan also comprise co-extruded fibers which—in turn—comprise a fiber coremade of polyester having a high melting point and a fiber coatingcomprising a copolymer having a low melting point.

In summary, the roof lining according to the invention is particularlyadvantageous because no noxious fumes are emitted and can bemanufactured without the use of liquid adhesives which could lead tostains in the decor layer. Thanks to its simplicity the method ofmanufacture is particularly robust and stable. Trimming or adjusting theroof linings can be achieved in a simple manner.

1. Inner roof lining for a vehicle roof (A) having an air permeable corelayer (4), which core layer (4), on the vehicle roof side, comprises afirst air permeable stiffening layer (2) and on the passengercompartment side comprises a second air permeable stiffening layer (6),whereby the second stiffening layer (6) on the passenger compartmentside is provided with an air permeable décor layer(8), wherein the firststiffening layer (2) on the vehicle roof side comprises an airimpermeable backing layer (1), and wherein the first stiffening layer(2) and the core layer (4), as well as the core layer (4) and the secondstiffening layer (6) and the décor layer (8) are attached to each otherwith the aid of air permeable adhesive layers (3, 5, 7), whereby forproducing an acoustically optimized vehicle roof inner lining, thecombination of layers (5, 6, 7, 8) on the passenger compartment side ofthe core layer have a total air flow resistance in the range of 500Nsm⁻³<R_(t)<3500 Nsm⁻³ and an area weight of between 300 gr/m² to 800gr/m², and wherein the backing layer (1) is provided on the vehicle roofside with an embossed relief-like profile.
 2. The lining according toclaim 1, wherein the air permeable core layer (4) is made of athermoformable PU foam, having a thickness of 10 mm to 35 mm and adensity of 8 to 30 kg/m³.
 3. The lining according to claim 1, wherein atleast one of the stiffening layers (2,6) is a thermoplastically bondednonwoven, and having an area weight of 100 gr/m² to 250 gr/m² for thefirst stiffening layer (2) and an area weight of 150 gr/m² to 450 gr/m²for the second stiffening layer (6).
 4. The lining according to claim 3,wherein the thermoplastically bonded nonwoven is composed of at leaststiffening fibers, acoustically effective fibers and bonding fibers. 5.The lining according to claim 3, wherein at least one of the stiffeninglayers (2, 6) has a multi-layered structure and has one layer having ahigh tensile stiffness and one layer having a predetermined air flowresistance.
 6. The lining according to claim 1, wherein at least one ofthe adhesive layers (3,5,7) is made of a reticulating adhesive, anadhesive fiber layer (polypropyleneSMMS—Spunbond/Meltblown/Meltblown/Spunbond) or of a perforated and inparticular a slitted foil.
 7. The lining according to claim 1, consistsof an air impermeable nonwoven, having an area weight of between 20 to80 gr/m² and in particular 40 gr/m².
 8. The lining according to claim 1,wherein the backing layer (1) comprises an air impermeable foil having athickness of between 20 to 80 μm and of about 50 μm.
 9. The liningaccording to claim 1, wherein the decor layer (8) comprises a nonwoven,having an area weight of between 100 to 300 gr/m², or comprises an airpermeable fabric and/or foam.
 10. An inner lining according to claim 1in combination with a vehicle roof, wherein the inner lining is looselyadjacent to or is at least partially attached to, and in particularadhesed to said vehicle roof.
 11. The lining according to claim 1,wherein the combination of layers (5, 6, 7, 8) on the passengercompartment side of the core layer have an air flow resistance in therange of 900 Nsm⁻³<R_(t)<1900 Nsm⁻³.